As is known, arthroplasty surgery, and particularly vertebroplasty operations require an appropriate amount of material to be introduced in the specific area to be treated to reinforce the implant site.
Therefore, invasive procedures such as percutaneous vertebroplasty or the like interventions, aimed for example at reducing vertebral compressions, require materials having the highest biological and microbiological safety and compatibility with the human body.
The currently used materials in this branch of surgery include specific acrylic resins, usually composed of a generally monomeric liquid component, which is used as a solvent for polymerization of a powder.
The two components are first enclosed in two separate containers, and later premixed to be introduced in the bone or vertebral cavity to be treated.
The liquid is held in a suitable container, such as a plastic bag or a glass vial. This later must withstand the chemical action of the liquid contained therein and must further have adequate mechanical strength and sealing properties, due to the toxicity of commonly used monomers.
Later, as the container is opened, the liquid is poured into a container in which the powder was previously placed, and is mixed therewith.
The latter step is typically carried out by an operator by means of a paddle, which may be operated manually or though a suitable container cover, equipped with a paddle rotating arrangement.
The compound so obtained is finally introduced in a special delivery syringe and pressure injected into the bone cavity for implantation through a special needle.
These prior art solutions have the recognized drawback of exposing the operator with a highly reactive and toxic liquid, whose vapors may be freely released in the work environment, and be potentially inhaled by the operator. Also several steps are provided in which the bone cement is in contact with the outside environment. This can easily affect cement sterility whereby the cement may be an infection carrier for the patient being treated.
Furthermore, the preparation and the percentage composition of the mixture strongly depends on the particular skill of the operator, whereby there is the risk of obtaining cements that are not perfectly homogeneous or with the two phases in improper proportions.
A further drawback of these typical solutions is that the cement delivery pressure is exerted directly by the operator, thus resulting in a very low pressure. Hence, low-viscosity cements have to be used, whereas the medullary material has a much higher density.
In an attempt to overcome the above drawbacks, a number of different solutions have been provided, in which one or more of such drawbacks have been obviated.
U.S. Pat. No. 5,435,645, in the name of the same applicant, and WO-01/83094 disclose bone cement mixing devices, in which cement is prepared in sterile conditions. The liquid is first placed in a first chamber and later forced into a second chamber that contains the powder. Finally, the two phases are mixed by mechanical stirring. This further provides a cement having proper monomer and powder proportions.
Nevertheless, a drawback of these solutions is that the cement so obtained has to be still poured into a suitable delivery system, other than the device. This is a critical step of the process, as it is necessarily carried out in non-sterile conditions and as such can be a possible cause of contamination for the operator and the work environment.